Improve the header includes, cont'd

Also check in the modulemap file, and add a option to build with clang's
-fmodules.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/backend/gl/gl_common.h

@@ -3,6 +3,7 @@
 #include <GL/glext.h>
 
 #include "common.h"
+#include "log.h"
 
 // Program and uniforms for window shader
 typedef struct {